The use of GaAs transistors in electronic switches is known. Generally, GaAs transistors are preferred over PIN diodes because they may be readily integrated onto a monolithic integrated circuit, and because they dissipate negligible power in the ON state. Additionally, GaAs transistors are preferred over other field effect transistors because of their high frequency operating characteristics.
Nevertheless, the use of GaAs transistors often becomes impractical or impossible due to several inherent detriments. One such detriment stems from the realization that GaAs field effect transistors are depletion mode devices, which require a negative bias voltage (for an N-channel device) between the gate and source terminals to switch the transistor to the OFF state. Thus, an additional power supply is required to operate the switch. Secondly, currently available GaAs transistors have a drain-to-source breakdown voltage of approximately 18 Volts. Exceeding this breakdown voltage causes irreversible damage. Consequently, GaAs transistors may only be used to switch signals up to approximately three (3) Watts (assuming a fifty (50) Ohm load) without damaging or destroying the switch.
The GaAs switch described below, however, not only permits the switching of higher power signals, but also eliminates the need for an additional bias voltage supply by deriving the necessary bias voltage directly from the input signal to the switch.